The present invention relates to a gas phase process for preparing cycloaliphatic and aliphatic (hereinafter "(cyclo)aliphatic") triisocyanates.
Although the preparation of organic isocyanates by reacting amines with phosgene in the gas phase has been known for some time (see, e.g., Siefken, Justus Liebigs Ann. Chem. 562. 108 (1949).), such preparation has only been recommended for monoisocyanates (e.g., Ullmanns Encyklop adie der technischen Chemie, 4th ed. Vol. 13, page 353), (cyclo)aliphatic diisocyanates (EP-A-0,289,840 and German Patent Application P 44 12 327.2), or for the preparation of aromatic diisocyanates (DE-OS 4,217,019).
Although (cyclo)aliphatic triisocyanates are mentioned in the literature, these triisocyanates are not available on an industrial scale. In fact, these triisocyanates are not obtainable in commercial yields by the classical process of phosgenating the corresponding triamines in the liquid phase. This is due to the low yields of crude product and the mechanical problems encountered during preparation by this process.
Traditional phosgenation of 1,8-diamino-4-aminomethyloctane in the liquid phase yields 74% of the desired triisocyanate, with respect to the amine used (DE-C-3,109,276). The disadvantage of the process disclosed in DE-C-3,109,276 are both the low yield and mechanical problems. These mechanical problems indicate either that reliable stirring of the reaction mixture is very difficult or that extremely high dilution with solvents is required during phosgenation. These disadvantages may be partially reduced, according to the disclosures in Jp-A-60,233,043 and JP-A-60,233,044, by mixed phosgenation of the triamines with aromatic or aliphatic diamines. The disadvantage of each of these processes, however, is the necessity for separation by distillation of the two polyisocyanates formed and the inevitable production of the particular diisocyanate.